Work machines such as, for example, excavators, loaders, dozers, motor graders, and other types of heavy machinery use multiple hydraulic actuators to accomplish a variety of tasks. These actuators are typically velocity controlled based on an actuation position of an operator interface device. For example, an operator interface device such as a joystick, a pedal, or any other suitable operator interface device may be movable to generate a signal indicative of a desired velocity of an associated hydraulic actuator. When an operator moves the interface device, the operator expects the hydraulic actuator to move at an associated predetermined velocity. However, this predetermined velocity is set during manufacture of the work machine, generally without a load being applied to the hydraulic actuator. During operation of the work machine when a load applied against the hydraulic actuator is light, the hydraulic actuator may move at a velocity that substantially matches the operator's expected velocity. However, when the load applied against the hydraulic actuator is heavy, the hydraulic actuator may move at slower and unexpected or undesired velocity. Attempts to control the velocity of the hydraulic actuator regardless of loading have resulted in harsh or jerky movements of the hydraulic actuator.
One method of improving the predictability of hydraulic actuator velocity while providing smooth operation of the hydraulic actuator is described in U.S. Pat. No. 5,784,945 (the '945 patent) issued to Krone et al. on Jul. 28, 1998. The '945 patent describes an apparatus for determining a valve transform curve in a work machine fluid system. The fluid system includes a fluid actuator with a valve arranged to initiate movement of a load. A desired velocity is determined from a load control input device and a characteristic of an applied load (a weight or a position) is determined. A valve transform curve is then generated to achieve the desired velocity based on the characteristic of the applied load.
Although the apparatus of the '945 patent may improve velocity predictability of the fluid actuator under several classifications of loads, the apparatus of the '945 patent does not provide flexibility when operating different work tools attachable to the same work machine or when different operators are controlling the work machine. For example, one work tool may function optimally under a different input device position/load/command velocity relationship than another work tool attachable to the same work machine. Further, one work machine operator may expect or prefer a different input device position/load/command velocity relationship than another work machine operator. The apparatus of the '945 patent does not allow the input device position/load/command velocity relationship to be modified or selected for different work tool attachment configurations or according to operator preference.
The disclosed hydraulic control system is directed to overcoming one or more of the problems set forth above.